Designation: E278 − 01 (Reapproved 2015)´1

Standard Test Method for

Determination of Phosphorus in Iron Ores by
Phosphomolybdate Coprecipitation and Nitric Acid
Titrimetry1
This standard is issued under the fixed designation E278; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.

ε1 NOTE—Editorial corrections were made in 1.2 and Table 1.

E882 Guide for Accountability and Quality Control in the
Chemical Analysis Laboratory

1. Scope
1.1 This test method covers the determination of phosphorus in iron ores, concentrates, and agglomerates.

3. Terminology

1.2 This test method covers the determination of phosphorus in the range from 0.01 % to 1.00 %.

3.1 Definitions—For definitions of terms used in this test
method, refer to Terminology E135.

1.3 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
standard.
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the

responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

4. Summary of Test Method
4.1 The sample is dissolved in HCl and HNO3. After the
addition of HClO4, the solution is evaporated to strong fumes
to dehydrate the silica. The insoluble residue is filtered off,
ignited, and treated for the recovery of any contained phosphorus. Ammonium molybdate is added to precipitate phosphomolybdate. The precipitate is filtered off and washed free
from acid. It is then dissolved in an excess of standard sodium
hydroxide solution. The excess sodium hydroxide is titrated
with a standard solution of HNO3 using phenolphthalein as an
indicator.

2. Referenced Documents
2.1 ASTM Standards:2
D1193 Specification for Reagent Water
E50 Practices for Apparatus, Reagents, and Safety Considerations for Chemical Analysis of Metals, Ores, and
Related Materials
E135 Terminology Relating to Analytical Chemistry for
Metals, Ores, and Related Materials
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
E877 Practice for Sampling and Sample Preparation of Iron
Ores and Related Materials for Determination of Chemical Composition and Physical Properties

5. Significance and Use
5.1 This test method is intended to be used for compliance
with compositional specifications for phosphorus content. It is
assumed that all who use these procedures will be trained
analysts capable of performing common laboratory procedures
skillfully and safely. It is expected that work will be performed

in a properly equipped laboratory and that proper waste
disposal procedures will be followed. Appropriate quality
control practices shall be followed, such as those described in
Guide E882.

1
This test method is under the jurisdiction of ASTM Committee E01 on
Analytical Chemistry for Metals, Ores, and Related Materials and is the direct
responsibility of Subcommittee E01.02 on Ores, Concentrates, and Related Metallurgical Materials.
Current edition approved Nov. 15, 2015. Published December 2015. Originally
approved in 1965. Last previous edition approved in 2010 as E278 – 01 (2010)ɛ1.
DOI: 10.1520/E0278-01R15E01.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.

6. Interferences
6.1 Vanadium and arsenic, elements commonly found in
iron ores, coprecipitate with the phosphorus. Provisions for
their removal or elimination of their interference are included
in this test method.
6.2 Titanium tends to form an insoluble compound with
phosphorus and thus may cause low values for phosphorus.
Provision for its removal is included in this test method.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

1



E278 − 01 (Reapproved 2015)´1
7.14 Potassium Nitrate, Wash Solution (10 g ⁄L)—Dissolve
10 g of potassium nitrate (KNO3) in water, dilute to 1 L, and
mix.

7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be
used in all tests. Unless otherwise indicated, it is intended that
all reagents conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society where
such specifications are available.3 Other grades may be used,
provided it is first ascertained that the reagent is of sufficient
high purity to permit its use without lessening the accuracy of
the determination.

7.15 Potassium Permanganate Solution (25 g ⁄ L)—Dissolve 25 g of potassium permanganate (KMnO4) in water and
dilute to 1 L.
7.16 Sodium Carbonate (Na2CO3).
7.17 Sodium Hydroxide, Stock Solution—Dissolve 300 g of
NaOH in 1 L of water. Add a slight excess of barium hydroxide
(Ba(OH)2) to precipitate any carbon dioxide (CO2). Allow any
precipitate to settle out. Store the solution in a polyethylene
container.

7.2 Purity of Water—Unless otherwise indicated, references
to water shall be understood to mean reagent water as defined
by Type II of Specification D1193.
7.3 Ammonium Molybdate Solution (Acidic).

7.3.1 Solution No. 1—Transfer 100 g of molybdic acid
(85 % MoO3) to a 600–mL beaker containing 240 mL of water
and mix thoroughly. Add 140 mL of NH4OH while stirring
vigorously. When dissolution is complete, filter through a
medium paper, add 60 mL of HNO3, and cool.
7.3.2 Solution No. 2—Add 400 mL of HNO3 to 960 mL of
water in a 2-L beaker and cool.
7.3.3 Add Solution No. 1 to Solution No. 2 while stirring
constantly. Add 0.1 g of ammonium phosphate, dibasic
((NH4)2HPO4), and let stand at least 24 h before using. Use
only the clear supernatant liquid.

7.18 Sodium Hydroxide, Standard Solution (0.15 N)—
Transfer 20 mL of the clear, supernatant stock solution to a 1-L
flask. Dilute to the mark with freshly boiled and cooled water
and mix thoroughly. Standardize this solution against potassium acid phthalate. It is convenient to adjust the normality of
this standard solution to 0.148 N (1 mL = 0.0002 g P). Confirm
the phosphorus value by analyzing a standard of a known
phosphorus content, preferably an iron ore of similar composition. Protect the NaOH solution from CO2 by means of a
soda-lime or soda-asbestos tube.
7.19 Sulfurous Acid (H2SO3).

7.4 Ammonium Nitrate (NH4NO3)

8. Hazards

7.5 Ferric Chloride Solution—Dissolve 0.3 g of pure iron
wire in 25 mL of HCl (1 + 1). Oxidize by adding HNO3
dropwise to the hot solution. Cool, add 25 mL of HCl, dilute to
1 L and mix.


8.1 For precautions to be observed in this test method, refer
to Practices E50.

7.6 Ferrous Sulfate Solution—Dissolve 100 g of ferrous
sulfate (FeSO4·7H2O) in 1 L of H2SO4 (5 + 95).

9.1 Sampling—The gross sample shall be collected and
prepared in accordance with Practice E877.

7.7 Hydrobromic Acid (1 + 4)—Mix 20 mL of concentrated
hydrobromic acid (HBr, sp gr 1.49) with 80 mL of water.

9.2 Sample Preparation—The laboratory sample shall be
pulverized to pass a No. 100 (150-µm) sieve.

7.8 Hydrochloric Acid (1 + 1)—Mix equal volumes of concentrated HCl (sp gr 1.19) and water.

NOTE 1—Some ores, such as specular hematites, may require finer
grinding to pass a No. 200 (75-µm) sieve.

9. Sampling and Sample Preparation

7.9 Hydrofluoric Acid (sp gr 1.15)—Concentrated HF.

9.3 Sample Weight—Weigh approximately (within
6 25 mg) an amount of sample specified as follows:

7.10 Nitric Acid, Standard (0.15 N)—Transfer 10 mL of
clear and water white concentrated HNO3 (sp gr 1.42) to a 1-L

flask, dilute to the mark, and mix. Standardize this solution
against the standard sodium hydroxide (NaOH) solution using
phenolphthalein as indicator. If desired, this solution may be
made equivalent to the standard sodium hydroxide solution by
dilution with water.

Content of Phosphorus, %

Weight of Sample, g

0.01 to 0.10
0.11 to 0.50
0.51 to 1.00

2.0
1.0
0.5

10. Procedure
10.1 Transfer the test sample to a small dry weighing bottle
and place in a drying oven. After drying at 105 °C to 110 °C for
1 h, cap the bottle, and cool to room temperature in a
desiccator. Momentarily release the cap to equalize pressure
and weigh the capped bottle to the nearest 0.1 mg. Repeat the
drying and weighing until there is no further weight loss.
Transfer the test sample to a 400-mL beaker and reweigh the
capped bottle to the nearest 0.1 mg. The difference between the
two weights is the weight of the test sample.

7.11 Nitric Acid, Wash Solution (1 + 99)—Mix 10 mL of

concentrated HNO3 (sp gr 1.42) with 990 mL of water.
7.12 Perchloric Acid (70 %) (HClO4).
7.13 Phenolphthalein Indicator Solution—Dissolve 0.2 g of
phenolphthalein in 100 mL of ethanol.

3
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC, www.chemistry.org. For suggestions on the
testing of reagents not listed by the American Chemical Society, see the United
States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention,
Inc. (USPC), Rockville, MD, .

10.2 Moisten the test sample with a few milliliters of water
and add 25 mL of HCl for each gram of test sample. Cover and
digest below the boiling point until all soluble minerals are in
2


E278 − 01 (Reapproved 2015)´1
molybdate solution. Shake vigorously for 5 min and let stand
20 min or until the yellow precipitate has settled.

solution. Add 5 mL of HNO3 and 20 mL of HClO4 and
evaporate to strong fumes to dehydrate the silica. Cool, add
50 mL of water, and warm until soluble salts are in solution.
Filter and collect the filtrate in a 300-mL Erlenmeyer flask.
Wash the residue with HNO3 (1 + 99), and finally with hot
water until free from perchlorates. Evaporate the filtrate using
a low heat.


NOTE 4—If the precipitate is small it is advisable to allow it to stand 4 h
or overnight.

10.6 Presence of Vanadium—Adjust the volume of the
solution to 100 mL, cool to 15 °C, add 5 mL of the FeSO4
solution and swirl the flask to reduce the vanadium. Add 50 mL
of the ammonium molybdate solution, shake vigorously for
10 min, and let stand for 1 h or until the yellow precipitate has
settled (Note 4).

10.3 Ignite the paper and residue in a platinum crucible.
Cool, moisten with several drops of water and add 2 mL of
HClO4 and 5 mL of HF, and evaporate to complete dryness.
Fuse the residue with 3 g of Na2CO3. Place the crucible in a
250-mL beaker and add 100 mL of water. Heat to disintegrate
the melt and to dissolve all soluble salts. Remove, wash, and
police the crucible. Filter the alkaline solution through a
medium-texture paper and collect the filtrate in the 400-mL
beaker. Wash the residue with hot water and discard. Acidify
the filtrate with HCl, add 5 mL of the ferric chloride (FeCl3)
solution, and render the solution alkaline to litmus with
NH4OH. Boil for 1 min to coagulate the precipitate. Filter and
wash the residue with hot water. Discard the filtrate. Place the
flask containing the evaporated filtrate from 10.2 underneath
the funnel. Dissolve the residue through the paper with 10 mL
of warm HCl (1 + 1) and wash with hot water. Discard the
paper and evaporate the solution to fumes of HClO4.

10.7 Filter the precipitate obtained in accordance with 10.5
or 10.6 on a close textured paper (Note 5). Wash the flask and

precipitate three times with 5-mL portions of the HNO3 wash
solution, and then with the KNO3 wash solution until free from
acid, as indicated by a litmus paper test. Since the yellow
precipitate tends to climb, direct the jet of the wash solution
around the edge of the paper and spirally down.
NOTE 5—A filtering crucible or smooth funnel plus perforated disk with
a macerated paper pulp pad may be used if desired.

10.8 Return the paper and precipitate to the Erlenmeyer
flask, add 25 mL of water (CO2-free), and an excess of 5 mL of
0.15 N NaOH solution. Shake or stir to break up the paper and
to dissolve the precipitate. Wash down the sides of the flask,
add three drops of the phenolphthalein indicator solution, and
titrate the excess NaOH with the 0.15 N HNO3.

NOTE 2—If the test sample is high in manganese, manganese dioxide
(MnO2) may precipitate when the solution is evaporated to HClO4 fumes.
If this occurs, the MnO2 can be redissolved by the addition of a crystal of
sodium nitrite (NaNO2) when the perchlorates are dissolved in water.
NOTE 3—If arsenic is known to be present, concentrate the solution in
the Erlenmeyer flask to approximately 75 mL, add 20 mL of HBr (1 + 4),
and evaporate to strong fumes. Cool, wash down the sides of the flask with
20 mL of water and again evaporate to fumes.

10.9 Blank—Carry along with the test sample a reagent
blank through all the steps of the procedure using the same
amounts of all reagents.
11. Calculation

10.4 Cool, add 50 mL of water, and warm to dissolve the

salts. Add an excess of several drops of KMnO4 solution and
boil the solution for several minutes. Add, dropwise, enough of
a solution of H2SO3 to reduce any KMnO4 or precipitated
MnO2. Boil to expel the SO2, cool, and add NH4OH until a
small precipitate of ferric hydroxide (Fe(OH)3) persists on
shaking or stirring. Add HNO3 until the precipitate just
dissolves on shaking, then 3 mL to 5 mL in excess. Add 10 g of
NH4NO3 and shake to dissolve the salts.

11.1 Calculate the percent of phosphorus as follows:
Phosphorus, % 5 100

TABLE 1 Statistical SummaryA

0.009
0.028
0.031
0.044
0.086
0.596

Standard Deviation
WithinLaboratory

BetweenLaboratories

0.0007
0.0008
0.0012
0.0017

0.0014
0.0106

0.0008
0.0008
0.0016
0.0018
0.0027
0.0106D

Reproducibility,
RC

Number of
Participating
Laboratories

0.0021
0.0024
0.0045
0.0051
0.0075
0.0300

5
7
7
7
7
7


G

(1)

where:
A = standard NaOH solution used, mL,
B = standard HNO3 required for titration of the excess of
NaOH in the test sample, mL,
C = standard NaOH solution equivalent to 1 mL of the
standard HNO3, mL,
D = standard NaOH solution required for blank
determination, mL,
E = standard HNO3 required for titration of the excess
NaOH in blank determination, mL,
F = phosphorus equivalent of the standard NaOH solution,
g/mL, and
G = weight of test sample used.

10.5 Absence of Vanadium—Adjust the volume to 150 mL
and the temperature to 20 °C and add 50 mL of the ammonium

Average,B
%

@ ~ A 2 BC! 2 ~ D 2 EC! # F

12. Precision and Bias4
12.1 Precision—Table 1 indicates the precision of the test
method as determined by Practice E691. To interpolate for

reproducibility factors, R, between 0.009 % and 0.60 % phosphorus (P), the following relationship may be used:

A

Calculations based on Practice E691.
Each percentage represents a different kind of iron ore.
Reproducibility factor, R, obtained by multiplying the between-laboratory standard deviation by 2 œ2 .
B

C

D

4
Supporting data have been filed at ASTM International Headquarters and may
be obtained by requesting Research Report RR:E16-174.

Provisional calculation of between-laboratories standard deviation was 0.0089.

3


E278 − 01 (Reapproved 2015)´1
R 5 0.01310.0781~ % P ! 2 0.0504 ~ % P ! 2

13. Keywords

(2)

12.2 Bias—There was no significant bias in the determinations made for an NIST certified reference material, NBS 27d,

certified at 0.028 % phosphorus. An additional CRM,
NBS 27c, certified as having 0.042 % phosphorus, was analyzed by two laboratories as having 0.038 % or 0.041 %
phosphorus.

13.1 agglomerates; concentrates; iron ore; phosphorus; related materials; titrimetric phosphorus

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